In recent years, from a perspective of preserving the environment, it is becoming popular to use a power generating apparatus of renewable energy type such as a wind turbine generator utilizing wind power and a power generating apparatus utilizing tidal current, ocean current or river current. In the power generating apparatus of renewable energy type, the kinetic energy of the wind, tidal current, river current or the like is converted to the rotation energy of the rotor and the rotation energy of the rotor is then converted into electric power by the generator.
In this type of power generating apparatus of renewable energy type, when there is a fault event in the apparatus itself or peripheral devices, an emergency stop is activated to avoid damages, life decline, or performance decline of the device and further to ensure the safety.
A method of stopping a power generating apparatus of renewable energy type, disclosed in Patent Literature 1 is a wind turbine generator which decelerates a rotor using a mechanical brake. Another method disclosed in Patent Literature 2 is to decelerate a blade by controlling its pitch angle toward a feathering position using a pitch control unit. As a method with a combination of the above methods, Patent Literature 3 proposes to use a pitch brake by a pitch angle control of the blade along with a mechanical brake.
In recent years, a power generating apparatus of renewable energy type using a hydraulic transmission with a combination of a hydraulic pump and a hydraulic motor is gaining popularity.
For instance, Patent Literature 4 provides a wind turbine generator equipped with a hydraulic transmission with a combination of a hydraulic pump driven by rotation of the rotor and a hydraulic motor connected to a generator. In this wind turbine generator, the hydraulic pump and the hydraulic motor are connected via an operating oil flow path and rotation energy of the rotor is transmitted to the generator via the hydraulic transmission.